import java.util.LinkedList;
import java.util.Queue;

public class BinaryTree {

    static class TreeNode {
        public char val;
        public TreeNode left; //左孩子的引用
        public TreeNode right; //右孩子的引用

        public TreeNode(char val) {
            this.val = val;
        }
    }


    // 创建一棵二叉树 返回这棵树的根节点
    public TreeNode createTree() { 
        TreeNode A = new TreeNode('A');
        TreeNode B = new TreeNode('B');
        TreeNode C = new TreeNode('C');
        TreeNode D = new TreeNode('D');
        TreeNode E = new TreeNode('E');
        TreeNode F = new TreeNode('F');
        TreeNode G = new TreeNode('G');
        TreeNode H = new TreeNode('H');
        A.left = B;
        A.right = C;
        B.left = D;
        B.right = E;
        C.left = F;
        C.right = G;
        E.right = H;
        return A;
    }

    // 前序遍历 根左右 
    public void preOrder(TreeNode root) {
        if(root == null){
            return;
        }
        System.out.print(root.val + " ");
        preOrder(root.left);
        preOrder(root.right);
    }

    // 中序遍历 左根右
    public void inOrder(TreeNode root) {
        if(root == null){
            return;
        }
        inOrder(root.left);
        System.out.print(root.val + " ");
        inOrder(root.right);
    }

    // 后序遍历 左右根
    public void postOrder(TreeNode root) {
        if(root == null){
            return;
        }
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val + " ");
    }

    public static int countSize = 0;

    // 获取树中节点的个数：遍历思路 O(N)
    // 遍历到节点 只要不为空，计数器加1
    public void size(TreeNode root) {
        if(root == null){
            return;
        }
        countSize++;
        size(root.left);
        size(root.right);
    }

    // 获取节点的个数：子问题的思路
    // 整棵树的节点个数 = 左子树的节点个数 + 右子树的节点个数 + 1
    public int nodeSize(TreeNode root) {
        if(root == null){
            return 0;
        }
        return nodeSize(root.left) + nodeSize(root.right) + 1;
    }

    public static int leafCount = 0;

    // 获取叶子节点的个数：遍历思路
    //root.left == null && root.right == null count++
    public void getLeafNodeCount1(TreeNode root) {
        if(root == null){
            return;
        }
        if(root.left == null && root.right == null){
            leafCount++;
        }
        getLeafNodeCount1(root.left);
        getLeafNodeCount1(root.right);
    }

    // 获取叶子节点的个数：子问题
    // 整棵树的叶子节点个数 = 左子树的叶子节点个数 + 右子树的叶子节点个数
    public int getLeafNodeCount2(TreeNode root) {
        if(root == null){
            return 0;
        }
        if(root.left == null && root.right == null){
            return 1;
        }
        return getLeafNodeCount2(root.left) + getLeafNodeCount2(root.right);
    }

    // 获取第K层节点的个数
    // 求A的第3层 等于 求B的第2层. 左子树+右子树
    public int getKLevelNodeCount(TreeNode root, int k) {
        if(root == null){
            return 0;
        }
        if(k == 1){
            return 1;
        }
        return getKLevelNodeCount(root.left,k-1) + getKLevelNodeCount(root.right,k-1);
    }

    // 获取二叉树的高度 时间复杂度：O(N)
    // 左 右子树高度的最大值 + 1（自身）
    public int getHeight(TreeNode root) {
        if(root == null){
            return 0;
        }
        return Math.max(getHeight(root.left),getHeight(root.right)) + 1;
    }

    // 检测值为value的元素是否存在
    public TreeNode find(TreeNode root, char val) {
        if(root == null){
            return null;
        }
        if(root.val == val){
            return root;
        }
        TreeNode ret = find(root.left,val);
        if(ret != null){
            return ret;
        }
        TreeNode ret2 = find(root.right,val);
        if(ret2 != null){
            return ret2;
        }
        return null;
    }

    //层序遍历
    public void levelOrder(TreeNode root) {
        if(root == null){
            return;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()){
            TreeNode cur = queue.poll();
            System.out.print(cur.val + " ");
            if(cur.left != null){
                queue.offer(cur.left);
            }
            if(cur.right != null){
                queue.offer(cur.right);
            }
        }
    }

    // 判断一棵树是不是完全二叉树
    public boolean isCompleteTree(TreeNode root) {
        if (root == null) {
            return true;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            TreeNode cur = queue.poll();
            if(cur != null) {
                queue.offer(cur.left);
                queue.offer(cur.right);
            }else{
                break;
            }
        }
        //判断队列中剩余的元素是不是都是空
        while (!queue.isEmpty()) {
            TreeNode cur = queue.poll();
            if (cur != null) {
                return false;
            }
        }
        return true;
    }

}